I have had my IPhone 4s for a few weeks and I try to add contacts and events but I can't. There is no + (add) button on the contacts and the + (add) button is grey and when I press it noting happens.
I had this happen on my Calendar. Go into the app switcher and close out the apps that you are having problems with, and then reopen them and try again. If that doesn't work then try closing the apps and then rebooting your phone. Hope it's a simple fix.
Let me know if it works.